In a series of three or more items, use a comma before the final and or or to avoid potentially changing the meaning of the sentence. This comma is called a serial comma or an Oxford comma.
Recommended: Locations are divided into zones, regions, and multi-regions.
Not recommended: Locations are divided into zones, regions and multi-regions.
Commas after introductory words and phrases
In general, place a comma after an introductory word or phrase.
Recommended: Finally, only groups that contain parameters appear in this list.
Recommended: Based on the requirements of your game, you can implement this method to update game information.
Commas separating two independent clauses
When a coordinating conjunction (and, but, or, nor, for, so, or yet) separates two independent clauses, insert a comma after the first clause (before the conjunction) unless both clauses are very short.
Recommended: The libraries make feed creation easier, and they ensure that only valid feeds are produced.
Not recommended: The libraries make feed creation easier and they ensure that only valid feeds are produced.
Recommended: Type your ID and click OK.
Not recommended: Type your ID, and click OK.
Commas separating independent from dependent clauses
When an independent clause and a dependent clause are separated by a coordinating conjunction, insert a comma only if the sentence could be misunderstood without one.
Recommended: Direct-access flags are plain variables and can be read directly.
Not recommended: Direct-access flags are plain variables, and can be read directly.
Recommended: The manager acknowledged the last team member who entered the room, and started the meeting.
Not recommended: The manager acknowledged the last team member who entered the room and started the meeting.
Set off other kinds of clauses
It's often a good idea to set off certain kinds of clauses with a comma or other punctuation for clarity.
A couple of specific places where commas are a good idea:
- In general, put a comma before the word which at the start of a nonrestrictive clause. For more information about this topic, see this guide's section on relative pronouns and Grammar Girl's page on which versus that.
- In general, put a semicolon or a period or a dash before a conjunctive adverb, such as otherwise, however, or therefore, and put a comma after the conjunctive adverb.
In general, don't use a comma before the causal conjunction because unless it is being used at the start of a nonrestrictive clause. For more information, see the Chicago Manual of Style Q&A entry on using commas with because.
|Name of the group, which has a maximum length of 200 characters.||Name of the group which has a maximum length of 200 characters.|
|The variable must have a value; otherwise, the server returns an error.||The variable must have a value otherwise the server returns an error.|
|You can use the same key name in multiple backend services and backend buckets because each set of keys is independent of the others.||You can use the same key name in multiple backend services and backend buckets, because each set of keys is independent of the others.|
For information about punctuating numbers, see Commas and decimal points in numbers.
For information about punctuating examples, see Format examples.